U.S. patent number 10,450,975 [Application Number 14/738,832] was granted by the patent office on 2019-10-22 for skip-fire fuel injection system and method.
This patent grant is currently assigned to WESTPORT POWER INC.. The grantee listed for this patent is Westport Power Inc.. Invention is credited to Jeffrey J. Thompson, Alain M. J. Touchette.
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United States Patent |
10,450,975 |
Touchette , et al. |
October 22, 2019 |
Skip-fire fuel injection system and method
Abstract
A cycle-by-cycle skip-fire fuel-injection technique for
pilot-ignited engines involve skip-firing selected combustion
chambers when a low load condition is determined and modulating the
fuel delivery to maintain the requisite engine power, while
reducing pilot fuel quantity to a predetermined minimum. Overall
pilot fuel consumption is thereby reduced.
Inventors: |
Touchette; Alain M. J.
(Vancouver, CA), Thompson; Jeffrey J. (Vancouver,
CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Westport Power Inc. |
Vancouver |
N/A |
CA |
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Assignee: |
WESTPORT POWER INC. (Vancouver,
CA)
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Family
ID: |
47664738 |
Appl.
No.: |
14/738,832 |
Filed: |
June 13, 2015 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20160017824 A1 |
Jan 21, 2016 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/CA2013/050958 |
Dec 12, 2013 |
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Foreign Application Priority Data
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Dec 14, 2012 [CA] |
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2798599 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02D
41/0027 (20130101); F02D 41/3058 (20130101); F02D
17/02 (20130101); F02D 41/406 (20130101); F02D
41/403 (20130101); F02D 41/0087 (20130101); Y02T
10/40 (20130101); Y02T 10/44 (20130101); F02B
2075/1824 (20130101) |
Current International
Class: |
F02D
41/00 (20060101); F02D 41/40 (20060101); F02D
17/02 (20060101); F02D 41/30 (20060101); F02B
75/18 (20060101) |
Field of
Search: |
;123/481 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1078662 |
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Jan 2002 |
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CN |
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101421500 |
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Apr 2009 |
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CN |
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1225321 |
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Jul 2002 |
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EP |
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9530085 |
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Nov 1995 |
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WO |
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2006017870 |
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Feb 2006 |
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WO |
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2010006321 |
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Jan 2010 |
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WO |
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2012024653 |
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Feb 2012 |
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WO |
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Other References
International Search Report of the International Searching
Authority dated Feb. 20, 2014, in connection with International
Application No. PCT/CA2013/050958. cited by applicant .
International Preliminary Report on Patentability dated Jun. 16,
2015, in connection with International Application No.
PCT/CA2013/050958. cited by applicant .
English translation of Search Report and First Office Action dated
Dec. 28, 2016 in connection with the corresponding Chinese Patent
Application No. 201380071024.X. cited by applicant .
First Office Action dated Dec. 28, 2016 in connection with the
corresponding Chinese Patent Application No. 201380071024.X. cited
by applicant .
Supplementary European Search Report dated Dec. 16, 2016, in
connection with the corresponding European Patent Application No.
13862956.3. cited by applicant.
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Primary Examiner: Staubach; Carl C
Attorney, Agent or Firm: Mager; Carie C.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of International Application No.
PCT/CA2013/050958 having a filing date of Dec. 12, 2013, entitled
"Skip-Fire Fuel Injection System and Method", which claimed
priority benefits from Canadian patent application No. 2,798,599
filed on Dec. 14, 2012. The '958 international application is
hereby incorporated by reference in its entirety.
Claims
What is claimed is:
1. A method of skip-firing an engine system wherein said engine
system comprises a plurality of combustion chambers and a
fuel-injection system configured to directly inject a gaseous main
fuel into each of said combustion chambers and a different pilot
fuel for triggering combustion of said gaseous main fuel, whereby
said fuel-injection system is capable of injecting said main fuel
into said combustion chamber after an associated air intake valve
is closed, said steps of said method comprising: (a) detecting when
said engine system is experiencing a predetermined low load
condition for applying a skip-fire injection mode; (b) determining
and selecting at least one combustion chamber of said plurality of
combustion chambers designated for skip-firing during a next cycle;
(c) skip-firing said selected at least one combustion chamber for a
given duration; (d) determining whether said engine system
continues experiencing said low load condition during said given
duration; wherein said engine system is configured to change a
ratio of said pilot fuel to a total fuel quantity measured on an
energy basis at said predetermined low load condition when operated
with skip firing compared to said same engine system when operated
without skip-firing and wherein the predetermined low load
condition is met when an injector lower limit is reached for
consistently directly injecting an amount of fuel.
2. The method of claim 1, wherein when said engine system is not
experiencing said low load condition during said given duration the
method further comprises; (e) returning said plurality of
combustion chambers to a normal injection mode.
3. The method of claim 1, further comprising: (e) injecting at
least some of said main fuel and said pilot fuel into said
combustion chamber after closing of an associated intake valve,
whereby timing for delivery of said at least some of said main fuel
is selected to be late cycle to prevent premature ignition.
4. The method of claim 1, further comprising (e) separately
injecting at least some of said main fuel and said pilot fuel into
said combustion chamber after closing of an associated intake valve
through one body of a fuel injection assembly, whereby timing for
delivery of said at least some of said main fuel is selected to be
late cycle to prevent premature ignition.
5. The method of claim 1, wherein said selecting at least one
combustion chamber of said plurality of combustion chambers
designated for skip-firing involves following a predetermined
cycle-by-cycle skip-firing pattern that reduces undesirable
vibrations in said engine system.
6. The method of claim 1, wherein said pilot fuel comprises diesel
fuel.
7. The method of claim 1, wherein said given duration comprises a
switching period having sufficient time for facilitating detecting
and selecting said at least one combustion chamber for skip-fire
during the next cycle.
8. The method of claim 1, wherein said engine system is configured
to inject the ratio as a lower ratio of said pilot fuel to said
total fuel quantity measured on an energy basis at said
predetermined low load condition when operated with skip firing
compared to said same engine system when operated without
skip-firing.
9. The method of claim 1, wherein, under certain predetermined load
conditions, said engine system is operable in a mode when said
pilot fuel is the only fuel consumed by said engine system; and
further comprising reducing an amount of time that said engine
system is fuelled only with said pilot fuel by applying said
skip-fire injection mode.
10. A skip-fire fuel-injection engine system, comprising: (a) an
engine system configured to use a gaseous main fuel and a different
pilot fuel for triggering combustion of said gaseous main fuel,
wherein said engine system comprises: (i) a plurality of combustion
chambers; and (ii) a fuel injection system for directly injecting
said main fuel and said pilot fuel into each of said combustion
chambers whereby said fuel injection system is capable of injecting
said main fuel into said combustion chamber after an associated air
intake valve is closed, (b) a programmable electronic feedback and
control system in communication with said fuel injection system,
said programmable electronic feedback and control system configured
to: (i) detect when said engine system is experiencing a
predetermined low load condition associated with a skip-fire
injection mode; (ii) when said predetermined low load is detected,
determine and select at least one combustion chamber of said
plurality of combustion chambers designated for skip-firing during
a next cycle; (iii) skip-firing said selected at least one
combustion chamber for a given duration; (iv) determine whether
said engine system continues experiencing said low load condition;
wherein said engine system is configured to change a ratio of said
pilot fuel to a total fuel quantity measured on an energy basis at
said predetermined low load condition when operated with skip
firing compared to said same engine system when operated without
skip-firing and wherein the predetermined low load condition is met
when an injector lower limit is reached for consistently directly
injecting an amount of fuel.
11. The system of claim 10, wherein said programmable electronic
feedback and control system is further configured to: (v) deliver
at least some of said main fuel into a combustion chamber after
closing of an associated intake valve, whereby timing for delivery
of said at least some of said main fuel is selected to be late
cycle to prevent premature ignition; and (vi) control timing for
delivery of said pilot fuel independently from said timing for
delivery of said at least some of said main fuel.
12. The system of claim 10, wherein said pilot fuel on average
comprises less than 5% of a total fueling measured on an energy
basis.
13. The system of claim 10, wherein said given duration comprises a
switching period having sufficient time for facilitating detecting
and selecting said at least one combustion chamber for skip-fire
during the next cycle.
14. The system of claim 10, wherein said engine system is
configured to inject the ratio as a lower ratio of said pilot fuel
to said total fuel quantity measured on an energy basis at said
predetermined low load condition when operated with skip-firing
compared to said same engine system when operated without
skip-firing.
15. The system of claim 10, wherein, said engine system is operable
in a mode when said pilot fuel is the only fuel consumed by said
engine system and said programmable electronic feedback and control
system is further configured to reduce an amount of time that said
engine system is fuelled only with said pilot fuel by applying said
skip-fire injection mode.
16. The system of claim 10, wherein said programmable electronic
feedback and control system is further configured to deliver at
least some of said main fuel into a combustion chamber after
closing of an associated intake valve through one body of a fuel
injection assembly, whereby timing for delivery of said at least
some of said main fuel is selected to be late cycle to prevent
premature ignition; and said one body of said fuel injection
assembly comprises a first fuel injection valve that is operable to
inject said pilot fuel independently from a second fuel injection
valve that is operable to inject said main fuel; and said fuel
injection assembly comprises a concentric needle injector, with
said first injection valve having a needle concentric with a needle
of said second injection valve.
17. A method of fabricating a skip-fire fuel-injection engine
system, comprising: (a) providing an engine system having a
plurality of combustion chambers and a fuel injection system, said
engine system being operable for directly injecting a gaseous main
fuel and a different pilot fuel for triggering combustion of said
gaseous main fuel whereby said fuel injection system is capable of
injecting said main fuel into said combustion chamber after an
associated air intake valve is closed; and (b) providing a
programmable electronic feedback and control system in electronic
communication with said fuel injection system, said programmable
electronic feedback and control system configured to: (i) detect
when said engine system is experiencing a predetermined low load
condition associated with a skip-fire injection mode; (ii) when
said predetermined low load is detected, determine and select at
least one combustion chamber of said plurality of combustion
chambers designated for skip-firing during a next cycle; (iii)
skip-fire said selected at least one combustion chamber for a given
duration; (iv) determine whether said engine system continues
experiencing said low load condition during said given duration;
wherein said engine system is configured to change a ratio of said
pilot fuel to a total fuel quantity measured on an energy basis at
said predetermined low load condition when operated with skip
firing compared to said same engine system when operated without
skip-firing and wherein the predetermined low load condition is met
when an injector lower limit is reached for consistently directly
injecting an amount of fuel.
18. The method of claim 17, wherein said programmable electronic
feedback and control system is further configured to: (v) deliver
at least some of said main fuel into a combustion chamber after
closing of an associated intake valve, and whereby timing for
delivery of said at least some of said main fuel is selected to be
late cycle to prevent premature ignition; and control timing for
delivery of said pilot fuel independently from said timing for
delivery of said at least some of said main fuel.
19. The method of claim 17, wherein said programmable electronic
feedback and control system is further configured to follow a
predetermined cycle-by-cycle skip-firing pattern that reduces
formation of harmonic frequency vibrations in said engine system
when selecting at least one combustion chamber of said plurality of
combustion chambers designated for skip-firing.
Description
FIELD OF THE INVENTION
The present disclosure relates to skip-fire engine technologies.
More specifically, the present disclosure relates to skip-fire
fuel-injection engine technologies for engines fueled with two
different fuels.
BACKGROUND OF THE INVENTION
Many related art engine systems utilize skip-firing modes or
fueling modes. These skip-firing modes include various skip-firing
patterns and various fueling strategies, but they do not provide a
solution for increasing the diesel substitution factor (DSF), that
is, decreasing the amount of diesel fuel that is consumed and
replacing it with another fuel to provide the desired amount of
total energy to fulfill the demanded engine load. Because diesel
fuel is readily available, and its ignition properties are well
known, diesel fuel is often used as a pilot fuel for triggering
combustion of other fuels that are less readily ignited, such as
natural gas or other gaseous fuels. However, other substances, such
as dimethyl ether or kerosene, could be substituted as the pilot
fuel. Accordingly, references to "diesel" and "DSF" will be
understood to include fuels that can be employed as pilot fuels to
trigger the combustion of a different fuel, which is employed as
the main fuel. On average, the main fuel constitutes the majority
of the fuel that is consumed by the engine.
U.S. Pat. No. 5,553,575 relates to a "gas-fueled unthrottled
internal combustion engine" having an excess air ratio (lambda)
that is optimized by selecting automatically and continuously the
optimum fraction of combustion chambers firing (OFF) as a function
of engine operating parameters. Further lambda adjustment is
performed by suitable control of exhaust gas recirculation (EGR),
ignition timing, and/or turbo air bypass (TAB). More specifically,
the '575 patent discloses a dual-fuel system which can be fueled
with port-injected natural gas and an ignition assist system that
can consist of a spark plug or a fuel injector for introducing
pilot quantities of diesel fuel directly into the combustion
chamber. Port-injected natural gas is injected into the intake
port, upstream of the engine intake valve so that the natural gas
mixes with the intake air during the engine's intake and
compression stroke. If the mixture of natural gas and air detonates
prematurely during the compression stroke, this premature
detonation is commonly referred to as "engine knock" and this can
result in significant damage to the engine. To reduce the risk of
engine knock, engines normally reduce the compression ratio and/or
reduce the amount of natural gas and increase the amount of diesel
fuel that is consumed by the engine. Compared to a conventional
diesel engine, in which the fuel is injected directly into the
combustion chamber late in the compression stroke, forming a
stratified charge, fuel that is port-injected has more time to mix
with the air, forming a more homogeneous mixture. The '575 patent
also discloses that, for port-injected natural gas, it is important
to maintain lambda within a narrow range for the efficient
combustion of the homogeneous mixture and to avoid misfiring and
excessive production of NOx. Accordingly, the '575 patent is
directed to a method for controlling lambda; it is not directed
towards a method of reducing the amount of diesel fuel
consumed.
Like the '575 patent, U.S. Pat. No. 5,477,830 also relates to an
internal combustion engine with natural gas that is injected into
the intake air system, upstream of the combustion chamber intake
valves. However, the '830 patent is specifically directed to an
electronic fuel injection system for the precise distribution of
natural gas into each cylinder for engines that use a shared intake
port for a pair of cylinders. Duration and timing of the fuel
injection pulse and other injection strategies, such as a skip-fire
operation, are controlled and enabled. However, like the '575
patent, because the '830 patent is directed to a dual fuel engine
that teaches fumigating the natural gas to form a homogeneous
mixture and controlling the air-fuel mixture (lambda); its
objective is not increasing the DSF.
With an engine that injects a main fuel into the intake air system,
and injects a second fuel, such as diesel fuel directly into the
combustion chamber, there are times when the DSF is decreased (not
increased). For example, when the amount of port injected fuel is
limited to prevent, or at least reduce, engine knock, the amount of
injected diesel fuel is increased to satisfy the total amount of
energy needed for the commanded engine load and speed condition.
With engines such as those disclosed in the '575 patent and the
'830 patent it is common under some normal operating conditions for
the fuel delivered to the engine to comprise between 50% and 100%
diesel fuel.
Skip-fire techniques are utilized by some conventional gasoline or
diesel mono-fueled engines, but for engines that are fueled with
only one fuel, DSF is not applicable. Rather, there are various
other reasons for using skip-fire techniques combined with
different fuel injection strategies, for example, to reduce smoke
emissions, to increase boost pressure, and to adjust air to fuel
ratio.
U.S. Pat. No. 5,826,563 relates to a high horsepower locomotive
diesel engine that is operated in a skip-firing mode, wherein the
engine includes a plurality of individually controllable,
fuel-injected cylinders. The system senses that the engine is
operating in a low horsepower mode and has a low fuel demand. The
pattern selected for firing the cylinders is arranged such that all
cylinders of the engine are fired within a preselected number of
crankshaft rotations. The system also senses the engine air-fuel
ratio and adjusts the pattern of cylinders being fired so as to
maintain exhaust emissions below a preselected level. Additionally,
the pattern of fired cylinders can be adjusted to maintain engine
operating temperature and as a function of engine speed.
Accordingly, the '563 patent relates to skip-fire for the purpose
of adjusting the air to fuel ratio and adjusting the total fuel
limit value for reducing smoke emissions in locomotive diesel
systems.
U.S. Pat. No. 6,405,705 and continuation-in-part U.S. Pat. No.
6,823,835 both relate to a diesel engine having a plurality of
individually controllable fuel-injected cylinders that is operated
in a skip-firing mode to reduce smoke emissions during low power
operation. The system senses certain identified engine operating
parameters and, when these parameters exceed predetermined
thresholds for a predetermined time, skip-firing is implemented.
Upon implementation of skip-firing, the engine timing angle is
reset by a fixed angle and a multiplication factor is included in
the speed loop integrator to ensure that the appropriate fuel
volume value is injected into each cylinder immediately upon
initiation of skip-firing. The '705 patent relates to skip-fire in
conjunction with adjusting the air to fuel ratio and adjusting the
total fuel limit value for reducing smoke emissions in locomotive
engine systems, and the '835 patent relates to adding fuel from
skipped cylinders into fueled cylinders for adjusting air to fuel
ratio in order to maintain performance parameters.
U.S. Pat. No. 6,408,625 relates to an electric power generation
system which includes a back-up electric power generator driven by
a four-cycle internal combustion engine. The engine includes a
compressor along an intake pathway to deliver pressurized air to
the cylinders and a turbine along an exhaust pathway to power the
compressor when driven by exhaust discharged from the cylinders.
The engine is prepared to accept a generator load by increasing
boost pressure provided by the compressor. This increase in boost
pressure is accomplished by skip-firing the cylinders in a selected
pattern, thereby retarding ignition timing for the cylinders, or by
using a combination of these techniques. Accordingly, the '625
patent relates to a skip-firing technique for increasing boost
pressure.
U.S. Pat. No. 8,136,497 involves a method for improving starting of
an engine that can be repeatedly stopped and started to improve
fuel economy. In one embodiment, the method involves using
skip-fire when the engine is idling to reduce fuel consumption and
prevent the engine speed from overshooting the desired idle speed.
Another embodiment is disclosed whereby skip-fire is employed for
torque control.
U.S. Patent Application Publication No. 2011/0253113 relates to an
engine that is configured with an exhaust gas recirculation (EGR)
system, The EGR system comprises exhaust manifolds from one or more
cylinders being connected to an intake system, such cylinders being
referred to as donor cylinders. These donor cylinders are the
cylinders from which exhaust gas is recirculated to the intake. For
an engine which uses skip-fire, the '113 publication relates to
various methods and systems for operating an internal combustion
engine that has one or more donor cylinders and one or more
non-donor cylinders. Accordingly, depending upon the engine
operating conditions, the '113 publication is directed to methods
for choosing whether to skip either donor cylinders or non-donor
cylinders when skip-fire is commanded. For example, during an EGR
cooler heating mode, the system operates at least one of the donor
cylinders at a cylinder load that is sufficient to increase an
exhaust temperature for regenerating an EGR cooler and operates at
least one of the non-donor cylinders in a low-fuel or no-fuel
mode.
U.S. Pat. No. 8,131,447 relates to a variety of methods and
arrangements for improving fuel efficiency of internal combustion
engines, including selectively skipping combustion events so that
other working cycles can operate at a better thermodynamic
efficiency. A controller is used to dynamically determine the
chamber firings required to provide the engine torque based on the
engine's current operational state and conditions. The chamber
firings can be sequenced in real time or in near real time in a
manner that helps reduce undesirable vibrations of the engine.
While these background examples may relate to skip-fire techniques
in association with a variety of technical problems, they fail to
disclose an engine that injects two different fuels directly into
the combustion chamber, or methods for increasing the amount of one
fuel that is substituted for the other fuel. More specifically,
when diesel fuel is employed as a pilot fuel, none of these
background examples discloses increasing DSF and reducing overall
diesel pilot fuel consumption in direct-injection
compression-ignition engine systems.
SUMMARY OF THE INVENTION
The present disclosure generally involves systems and methods that
provide many beneficial features and advantages over the prior art,
including, significantly reducing overall pilot fuel consumption
for engines that use a pilot fuel to trigger the ignition of a
different fuel that serves as the main fuel, especially for
compression-ignition engine systems. The disclosed systems and
methods also involve a skip-fire fuel-injection strategy that
increases the pilot fuel substitution factor, referred to herein as
the DSF. Compared to engines that inject fuel into the intake port
or elsewhere upstream from the intake valve, when engines inject
fuel into the combustion chambers either via a pre-chamber or
directly, the fuel must be injected at higher pressures to overcome
the in-cylinder pressure that increases during the compression
stroke.
High-pressure direct-injection (HPDI) engine systems denote engine
systems that introduce at least some of the main fuel and the pilot
fuel into a combustion chamber during the compression stroke or
near the beginning of the power stroke (this injection timing being
referred to herein as "late cycle injection timing"). In an HPDI
engine system, the timing for injecting the fuel into the
combustion chamber is determined based on the desired timing for
ignition of the fuel, with the fuel burning in a stratified
combustion mode rather than a pre-mixed combustion mode. When a
fuel is injected directly into a combustion chamber there is
normally a time delay, referred to as the "ignition delay", between
the timing for start of injection and the timing for start of
ignition. Accordingly, in an HPDI engine system, the timing for
start of injection can be determined based upon the timing for
start of ignition, minus the ignition delay associated with
detected engine operating conditions so that the fuel ignites at
the desired time, thereby preventing premature detonation. For an
HPDI engine system, both fuels can be introduced into the
combustion chamber after the associated intake valve closes,
whether this is accomplished by way of being injected directly into
the combustion chamber or indirectly injected via a pre-chamber.
Engines that use port injection can be "knock limited," meaning
that a limit exists on the amount of fuel that can be safely
port-injected into the intake air system upstream from the
combustion chamber intake valve. Such port-injected engines use an
increased amount of directly-injected pilot fuel to constitute the
total amount of fuel that is needed on an energy basis. However,
for HPDI engine systems, reducing the amount of pilot fuel to that
which is needed for ignition of the main fuel is possible since
late cycle injection timing lowers the danger engine knock as the
fuel is not introduced into the combustion chamber until the
intended time for its ignition. A requisite total fueling is
mandated by a requisite engine power for a given engine operating
condition.
The present method comprises a skip-fire strategy, including a
cycle-by-cycle skip-firing pattern. Regardless of whether an engine
is a 2-stroke engine or a 4-stroke engine, a power stroke is
associated with each cycle. By controlling whether fuel is
introduced into a combustion chamber, the method involves
selectively skipping the firing in each cylinder on a
cycle-by-cycle basis. In preferred embodiments, the skipped
cylinders are selected in a pattern such that these skipped
cylinders reduce the formation of harmonic frequency vibrations in
the engine. In addition, the cycle-by-cycle skip-firing pattern
further comprises a switching period during a given cycle which
provides sufficient time for determining which cylinders to skip
for a subsequent cycle.
In addition, the present system and method involve a skip-fire
technique combined with a fuel-injection strategy for modulating
the fuel delivery. At low engine loads, as the total fuel
requirement decreases, a limit exists as to how much the pilot fuel
quantity can be reduced while also ensuring stable combustion. As
the pulse width of a pilot fuel injection event decreases, the
potential for variability is higher in the amount of pilot fuel
that is injected as other variables exist in addition to the
variability in the pulse width, such as the fuel pressure, cylinder
pressure, injector-to-injector differences, and
cylinder-to-cylinder differences. When the pulse width is very
short, the cycle-to-cycle differences in the amount of fuel
injected represent a larger fraction of the total fueling compared
to the cycle-cycle differences in the amount of fuel injected when
the commanded pilot fuel quantity is larger. Accordingly, at low
loads, to improve combustion stability, setting a lower limit on
the amount of pilot fuel that is commanded is preferable. For
engines that do set a lower limit on the amount of pilot fuel, by
using a skip-fire technique, the overall amount of pilot fuel that
is consumed in the firing cylinders is lower than engines that do
not employ a skip-fire technique. It is noteworthy that the DSF can
be increased in part because the amount of pilot fuel is determined
mainly by the amount needed for acting as a pilot fuel and
achieving stable combustion. Unlike prior engines, the amount of
pilot fuel is not determined by the energy needed to satisfy the
engine load.
The present method of skip-firing an engine system wherein the
engine system has a plurality of combustion chambers, a
fuel-injection system for delivering fuel to each combustion
chamber, and is operated with a main fuel and a pilot fuel,
comprises: detecting whether the engine is experiencing a
predetermined low load condition for applying a skip-fire injection
mode; when the predetermined low load condition is detected,
determining and selecting at least one combustion chamber of the
plurality of combustion chambers designated for skip-firing during
a next cycle; skip-firing the selected at least one combustion
chamber for a given duration whereby pilot fuel substitution is
increased and overall pilot fuel consumption is reduced;
determining whether the engine continues experiencing the low load
condition during the given duration; and, if so, repeating
determining and selecting at least one combustion chamber of the
plurality of combustion chambers to skip-fire during the next
cycle, and if not, returning the plurality of combustion chambers
to a normal injection mode.
The disclosed method also comprises at least one of: selecting a
different one or more combustion chambers for skip-firing in the
following cycle; continuing to skip-fire the same selected
combustion chamber(s) for a predetermined number of cycles or for a
predetermined time duration, or when a plurality of combustion
chambers are selected; continuing to skip-fire a select one or more
of the same selected combustion chambers in addition to skip-firing
a select one or more of different combustion chambers.
After completing the predetermined number of cycles or completing
the predetermined time duration, the method further comprises
determining whether the engine continues to experience the low load
condition; and, if so, repeat determining and selecting at least
one combustion chamber of the plurality of combustion chambers to
skip-fire during the next cycle, and if not, ending the skip-fire
mode and returning the plurality of combustion chambers to a normal
injection mode.
The present skip-fire fuel-injection engine system generally
comprises an engine system, such as a compression-ignition engine
system, for example, a diesel engine system, modified and operable
for fueling with a main fuel and a pilot fuel. The engine system
has a plurality of combustion chambers and a fuel injection system,
preferably for separate and independent injection of the pilot fuel
and the main fuel. In preferred embodiments, the pilot fuel can be
diesel fuel and the main fuel can be natural gas, or other suitable
gaseous fuels, such as methane, propane, hydrogen, and mixtures
thereof. The engine system further comprises a feedback and control
system in electronic communication with the fuel injection system.
The feedback and control system is adapted to: determine whether
the engine is experiencing a low load condition for applying a
skip-fire injection mode; determine and select at least one
combustion chamber of the plurality of combustion chambers
designated for skip-firing during a next cycle.
The present method of fabricating a skip-fire engine system
generally comprises providing an engine system that employs a pilot
fuel to trigger the ignition of a main fuel, or modifying a diesel
engine system for fueling with a main fuel that uses a pilot fuel
to trigger ignition of the main fuel. The engine system has a
plurality of combustion chambers and a fuel injection system for
introducing the pilot fuel and the main fuel into each one of the
respective combustion chambers. In preferred embodiments the fuel
injection system injects the pilot fuel and the main fuel directly
into the combustion chamber. However, the method could also
comprise providing a pre-chamber into which one or both fuels are
injected. In either case, the common feature is that late cycle
injection is enabled after the intake valve is closed. The present
fabrication method also comprises providing a feedback and control
system in electronic communication with the fuel injection system
the diesel engine system. The feedback and control system is
adapted to: determine whether the engine is experiencing a low load
condition for applying a skip-fire injection mode; determine and
select at least one combustion chamber of the plurality of
combustion chambers designated for skip-firing during a next cycle;
skip-fire the selected at least one combustion chamber for a given
duration; determine whether the engine continues experiencing the
low load condition during the given duration; and, if so, repeat
determining and selecting at least one combustion chamber of the
plurality of combustion chambers to skip-fire during the next
cycle, and if not, return the plurality of combustion chambers to a
normal injection mode. A normal injection mode is defined herein to
be a mode in which pilot fuel and main fuel are delivered to each
of the engine's respective combustion chambers at a respective
timing so that each of the engine's pistons is doing substantially
the same amount of work for a given operating condition.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram illustrating an engine system with a
plurality of cylinders, with a fuel injector for injecting a pilot
fuel and a main fuel into each combustion chamber.
FIG. 2A is a graph illustrating command signals over time for
injection fuel into a combustion chamber for a low load operation
mode of an engine system without a skip-fire fuel-injection
operation mode.
FIG. 2B is a graph illustrating command signals over time for
injecting fuel into a combustion chamber for a low load operating
mode with a skip-fire fuel-injection operation mode of an engine
system.
FIG. 3 is a cross-sectional view of one cylinder, illustrating a
portion of an HPDI engine system suitable for use in a skip-fire
operation mode.
FIG. 4A is a graph illustrating a ratio of pilot fuel to main fuel
as a function of power for an engine system.
FIG. 4B is a graph illustrating torque as a function of engine
speed for an engine system.
FIG. 5 is a flowchart illustrating a skip-fire fuel-injection
method.
FIG. 6 is a flowchart illustrating a method of fabricating an
engine system.
Corresponding reference characters indicate corresponding
components. Elements in the figures are illustrated for simplicity
and clarity and have not necessarily been drawn to scale. For
example, the dimensions of some of the elements in the figures can
be emphasized relative to other elements for facilitating
understanding of the various presently disclosed embodiments. Also,
common, but well-understood, elements that are useful or necessary
in commercially feasible embodiments are often not depicted in
order to facilitate a less obstructed view of the various
embodiments.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENT(S)
Referring to FIG. 1, a schematic diagram illustrates engine system
100, such as a compression-ignition engine system, for example, a
diesel engine system. In this example, the engine has six cylinders
10 that each has two associated fuel injectors mounted to deliver
fuel into the combustion chamber defined by each cylinder. Pilot
fuel injector 70' is connected to pilot fuel rail 72' and pilot
fuel is supplied to pilot fuel rail 72' from pilot fuel supply
system 74', which includes pilot fuel pump 76' and pilot fuel
storage tank 78'. Main fuel injector 70'' is connected to main fuel
rail 72'' and main fuel is supplied to main fuel rail 72'' from
main fuel supply system 74'', which includes main fuel pump 76''
and main fuel storage tank 78''. In FIG. 1 pilot fuel injector 70'
and main fuel injector 70'' are shown in separate bodies, but as
shown in FIG. 3, the two injectors can be integrated into a single
body. In the illustrated embodiments, because the main fuel is
injected directly into the respective combustion chambers, at least
some of the main fuel can be injected after the respective intake
valves are closed, with the timing being determined to prevent, or
at least reduce the chance of, the formation of a combustible
mixture that ignites prematurely to cause engine knock.
During a normal operating mode, a normal injection mode is
employed, with the total fueling delivered to each cylinder 10
comprising a pilot fuel quantity A and a main fuel quantity B with
substantially the same amount of fuel and with substantially the
same timing for each cylinder for the various operating conditions.
In preferred embodiments, the pilot fuel comprises a diesel fuel,
preferably in a range of approximately 5% of the total fueling,
measured on an energy basis. The main fuel can comprise compressed
natural gas, preferably in a range of approximately 95% of the
total fueling, measured on an energy basis. While the illustrated
engine system has six cylinders, it will be appreciated that other
engine systems with a plurality of combustion chambers can benefit
from this method. In the illustrated example, with a six-cylinder
engine, a normal injection mode during a normal operating mode
comprises modulating a predetermined minimum pilot fuel quantity
and modulating a main fuel quantity for each of the six cylinders
at a ratio that maintains a requisite engine power.
Engine system 100 comprises feedback control system 200 in
electronic communication with the fuel injection system. Feedback
control system 200 is adapted to detect whether engine system 100
is experiencing a predetermined low load condition associated with
a skip-fire injection mode. When a predetermined low load is
detected feedback control system 200 determines and selects at
least one combustion chamber of the plurality of combustion
chambers associated with cylinders 10 that is designated for
skip-firing during a next cycle. The feedback control system 200
skip-fires the selected at least one combustion chamber for a given
duration and then determines whether engine system 100 is
continuing to experience the low load condition during the given
duration. If engine system 100 is still experiencing the low load
condition, then feedback control system 200 repeat determining and
selecting at least one combustion chamber of the plurality of
combustion chambers to skip-fire during the next cycle. If engine
system 100 is not experiencing the low load condition, feedback
control system 200 returns the plurality of combustion chambers to
a normal injection mode.
Feedback control system 200 can control pilot fuel injector 70'
independently from its control of main fuel injector 70'' so that
the timing for injection of each fuel and the quantity of each fuel
injected can be determined to achieve the desired combustion
characteristics and increase the DSF. Because each fuel injector is
individually controlled, feedback control system 200 can be
programmed to follow a predetermined cycle-by-cycle skip-firing
pattern that reduces vibrations and avoids harmonic frequencies
when selecting at least one combustion chamber of the plurality of
combustion chambers that is designated for skip-firing.
While the skip-fire operation mode can cause irregular structural
loading of engine components such as the pistons and the
crankshaft(s); these effects are minimized, or at least reduced, at
low loads and have less influence on engines that have a greater
number of cylinders. In preferred embodiments, the main fuel
comprises a gaseous fuel, such as natural gas, that can be stored
as liquefied natural gas (LNG) or compressed natural gas (CNG); and
the pilot fuel comprises diesel fuel. The given duration for the
skip-fire injection mode comprises a switching period having
sufficient time for facilitating detecting and selecting the at
least one combustion chamber for skip-fire during the next
cycle.
FIGS. 2A and 2B illustrate how the disclosed skip-fire technique
increases the pilot fuel substitution factor, resulting in reduced
overall pilot fuel consumption. FIG. 2A shows the injector command
signals for a six cylinder engine system operated without
skip-firing. The cylinder numbers along the left hand side of the
figure represent cylinder firing order. Over the same time scale,
indicated by crank angle degrees, for each cylinder there is a
respective command signal for the pilot fuel, A.sub.1, A.sub.2,
A.sub.3, A.sub.4, A.sub.5 and A.sub.6, and a respective command
signal for the main fuel, B.sub.1, B.sub.2, B.sub.3, B.sub.4,
B.sub.5 and B.sub.6. Because a minimum quantity of pilot fuel is
needed for stable combustion, at lower load conditions there is a
minimum amount of pilot fuel that is delivered to the pilot fuel
injectors when the six cylinders are firing in a normal operating
mode. FIG. 2B shows the injector command signals for the same six
cylinder engine operated with skip-firing. In this example, no fuel
is delivered to half of the cylinders (A.sub.2', A.sub.4' and
A.sub.6') so while the same minimum amount of pilot fuel is
injected into each cylinder, pilot fuel consumption is reduced by
half, and the main fuel B.sub.2', B.sub.4' and B.sub.6' can be
increased to the cylinders that are firing to make up the energy
requirement to satisfy the demanded engine load. In this way, the
engine system is operable using a lower ratio of the pilot fuel to
a total fuel quantity measured on an energy basis at predetermined
low load conditions compared to the same engine system when
operated without employing a skip-fire operating mode. Like the
pilot fuel injectors, with the main fuel injectors there is also a
lower limit on the amount of fuel that can be consistently injected
so increasing the amount of main fuel that is injected into each
combustion chamber using the skip-fire technique also helps to
improve combustion stability.
Using the disclosed skip-fire technique and increasing DSF at low
load helps to improve the overall DSF. During operation over a
range of engine loads for a typical operating cycle for engines
used to power a vehicle, with the skip-fire technique, the pilot
fuel comprises approximately 5% or less of a total fueling measured
on an energy basis. The main fuel comprises approximately 95% or
more of a total fueling measured on an energy basis. Under certain
predetermined load conditions, the engine system can be operable in
a mode when the pilot fuel is the only fuel consumed by the engine
system. During skip-firing operating mode different patterns for
cylinder firing can be employed such that over time all cylinders
are fired. It is desirable to eventually fire each cylinder during
skip-firing operating mode so diesel accumulation in the injector
is reduced. Due to the pressure differential between gas and
diesel, diesel accumulation in the injector causes the diesel to
flow into the gas rail. For example, during one engine cycle
cylinders 1, 3 and 5 can be fired, and during the next engine cycle
cylinders 2, 4 and 6 can be fired. It is not a requirement that the
cylinders to be fired are changed from engine cycle to engine
cycle.
FIG. 3 is cross-sectional view of one cylinder of skip-fire
fuel-injection engine system 100 (see FIG. 1) that comprises a
plurality of cylinders, suitable for use in a skip-fire operation
mode. By example only, engine system 100 generally comprises:
cylinder 10 formed by cylinder walls 24 of engine block 25; piston
20 mechanically and rotatably coupled with a piston rod (not shown)
by way of a pin (not shown) disposed through opening 30; intake
manifold 40 for delivering air in direction I into combustion
chamber 50 by way of operation of intake valve 41; exhaust manifold
60 for delivering exhaust in direction E away from combustion
chamber 50 by way of operation of exhaust valve 61; and fuel
injector 70, being one component of a fuel injection system, for
delivering fuel to the combustion chamber. In the illustrated
embodiment, fuel injector 70 is designed to have two injector
assemblies in one body for injecting a pilot fuel, such as a diesel
pilot, and a main fuel, such as natural gas. In preferred
embodiments fuel injector 70 can comprise concentric needles with
one needle controlling the injection of the pilot fuel and another
needle controlling the injection of the main fuel. In another
embodiment, the fuel injector can inject the pilot fuel and the
main fuel together. In yet other embodiments (not shown) for
engines with more space to accommodate other arrangements, there
can be two separate injection valve assemblies in the same body
(for example, side by side and parallel to each other), or (as
shown in FIG. 1) two separate fuel injectors each with its own body
mounted separately.
FIG. 4A is a graph that illustrates a ratio R of pilot fuel to main
fuel (%) as a function of power P (hp) for an engine system
utilizing skip-fire, compared to the same data for an engine system
operating under the same conditions but without using skip-fire.
When engine system 100 is operating near idle at low power the
quantity of pilot fuel consumed relative to main fuel increases,
since a minimum quantity of pilot fuel is required for ignition.
Line 200 represents the ratio R as a function of power for engine
system 100 not operating in skip fire mode, and line 210 represents
the same relationship when engine system 100 switches to skip fire
mode at powers below P1. As can be seen by line 210, skip-firing
operating mode reduces the ratio of pilot fuel to main fuel,
thereby improving DSF.
Referring to FIG. 4B, this graph illustrates torque T as a function
of engine speed ES (rpm) for an engine system utilizing skip-fire,
compared to the same data for an engine system operating under the
same conditions but without using skip-fire. Engine system 100
operates in skip-fire mode in region 230, representing a low load
region of engine operation below line 220 representing torque T as
a function of engine speed ES.
FIG. 5 is a flowchart illustrates method M for skip-firing an
engine system such as the one shown in FIG. 1, the engine system
having a plurality of cylinders and a fuel-injection system, and
the engine system being operable with a main fuel and a pilot fuel.
In particular, the present skip-fire strategy comprises a
cycle-by-cycle skip-firing pattern (combustion chambers are
selectively skipped per cycle) which reduces the formation of
harmonic frequency vibrations in the engine system; and, when used
in combination with direct fuel injection or direct injection (both
pilot fuel and main fuel being delivered directly into the
combustion chamber or a pre-chamber after the intake valve closes
by way of a direct injector), injection timing is selected to
trigger ignition at the desired time, preventing, or at least
reducing the chance of, premature ignition and engine knock. In
addition, the present cycle-by-cycle skip-firing pattern further
comprises a switching duration during a given cycle which provides
a sufficient time period for determining which combustion chambers
to skip for the subsequent cycle.
Skip-fire method M for skip-firing an engine system comprises:
detecting engine load, as indicated by block 5001; determining when
the predetermined low load condition is detected, as indicated by
block 5002; when the predetermined low load condition is detected,
determining and selecting at least one combustion chamber of the
plurality of combustion chambers designated for skip-firing during
a next cycle, as indicated by block 5003; skip-firing the selected
at least one combustion chamber for a given duration, as indicated
by block 5004; determining whether the engine system continues
experiencing the low load condition during the given duration, as
indicated by block 5005; and, if so, repeating determining and
selecting at least one combustion chamber of the plurality of
combustion chambers to skip-fire during the next cycle, as
indicated by block 5006, and if not, returning the plurality of
combustion chambers to a normal injection mode, as indicated by
block 5007, thereby increasing a pilot fuel substitution factor and
reducing an overall pilot fuel consumption.
In preferred embodiments method M for skip-firing an engine system
further comprises delivering at least some of the main fuel into a
combustion chamber after closing of an associated intake valve,
whereby a timing for delivery of at least some of the main fuel is
selected to prevent, or at least reduce the chance of, premature
ignition; delivering the at least some of the main fuel and the
pilot fuel into the combustion chamber through a fuel injection
system; controlling timing for delivery of the pilot fuel
independently from timing for delivery of at least some of the main
fuel; and injecting the pilot fuel into the combustion chamber
separately from the main fuel.
In method M for skip-firing an engine system, selecting at least
one combustion chamber of the plurality of combustion chambers
designated for skip-firing further comprises following a
predetermined cycle-by-cycle skip-firing pattern that reduces
formation of harmonic frequency vibrations in the engine system.
The main fuel comprises a gaseous fuel, such as natural gas. The
pilot fuel comprises diesel fuel. The given duration comprises a
switching period having sufficient time for facilitating detecting
and selecting at least one combustion chamber for skip-fire during
the next cycle. The engine system is operable using a lower ratio
of the pilot fuel to a total fuel quantity measured on an energy
basis at the predetermined low load condition compared to the same
engine system when operated without skip-firing. With some engines
that use a pilot fuel to ignite a main fuel, when the engine load
decreases below a predetermined level, at which the minimum pilot
fuel amount provides all of the requisite energy to deliver the
commanded load, the amount of main fuel is reduced to zero. By
using the disclosed skip-fire operating mode, the amount of time
that an engine is fuelled only with pilot fuel is reduced because
the skip-fire operating mode extends the range of operation at low
operating loads where the main fuel provides at least some of the
energy required to deliver the demanded engine load. In preferred
embodiments, by using a skip-fire operating mode, overall pilot
fuel consumption can be reduced, so that the pilot fuel comprises
approximately 5% or less of a total fueling measured on an energy
basis. The main fuel comprises approximately 95% or more of a total
overall fueling measured on an energy basis. Under certain
predetermined load conditions, the engine system can still be
operable in a mode when the pilot fuel is the only fuel consumed by
the engine system, but the range of these conditions is reduced
compared to the same engine that does not use a skip-fire operating
mode.
FIG. 6 is a flowchart illustrating method M.sub.fab of fabricating
a skip-fire fuel-injection engine system. Method M.sub.fab
comprises: providing engine system 100 having a plurality of
combustion chambers 50 and a fuel injection system, engine system
100 being operable with a main fuel and a pilot fuel, as indicated
by block 8001; and providing a feedback and control system in
electronic communication with the fuel injection system, as
indicated by block 8002. The feedback and control system 200 is
adapted to: detect whether engine system 100 is experiencing a
predetermined low load condition associated with a skip-fire
injection mode; when the predetermined low load is detected,
determine and select at least one combustion chamber 50 of the
plurality of combustion chambers 50 designated for skip-firing
during a next cycle; skip-fire the selected at least one combustion
chamber 50 for a given duration; determine whether engine system
100 continues experiencing the low load condition during the given
duration; and, if so, repeat determining and selecting at least one
combustion chamber 50 of the plurality of combustion chambers 50 to
skip-fire during the next cycle, and if not, return the plurality
of combustion chambers 50 to a normal injection mode, whereby a
pilot fuel substitution factor is increased, and whereby overall
pilot fuel consumption is reduced.
In method M.sub.fab, feedback and control system 200 is further
adapted to: deliver at least some of the main fuel into a
combustion chamber 50 after closing of intake valve 41, such as an
associated intake valve, whereby a timing for delivery of the at
least some of the main fuel is selected to prevent, or at least
reduce the chance of, premature ignition; deliver at least some of
the main fuel and the pilot fuel into combustion chamber 50 through
a fuel injection system, such as integrated pilot and main fuel
injector 70; control timing for delivery of the pilot fuel
independently from the timing for delivery of at least some of the
main fuel; inject the pilot fuel into combustion chamber 50
separately from the main fuel; and follow a predetermined
cycle-by-cycle skip-firing pattern that reduces formation of
harmonic frequency vibrations in engine system 100 when selecting
at least one combustion chamber 50 of the plurality of combustion
chambers 50 designated for skip-firing.
In method M.sub.fab, the main fuel can comprise a gaseous fuel,
such as natural gas. The pilot fuel can comprise diesel fuel. The
given duration comprises a switching period having sufficient time
for facilitating detecting and selecting at least one combustion
chamber for skip-fire during the next cycle. The engine system is
operable using a lower ratio of the pilot fuel to a total fuel
quantity measured on an energy basis at the predetermined low load
condition compared to the same engine system when operated without
skip-firing. The pilot fuel can comprise approximately 5% or less
of a total fueling measured on an energy basis. The main fuel can
comprise approximately 95% or more of a total fueling measured on
an energy basis. Under certain predetermined load conditions, the
engine system is operable in a mode when the pilot fuel is the only
fuel consumed by the engine system with the range of these
conditions being reduced compared to an otherwise equivalent engine
that does not have a skip-fire operating mode.
The fuel injection system comprises a fuel injection assembly for
injecting a pilot fuel and a main fuel. In some embodiments, this
fuel injection assembly has one body, comprising a nozzle for
injecting the two fuels directly into the engine's combustion
chamber. In preferred embodiments the fuel injection assembly
comprises two separate and independently operable fuel injection
valves, one for the pilot fuel and one for the main fuel. These two
fuel injection valves can be concentric or parallel (side by side)
in the same body of the fuel injection assembly (as depicted in
FIG. 3). When there are two separate fuel injection valves, because
of the different mass densities of the two fuels, preferably, there
are two sets of orifices so the flow area through the orifices can
be made to accommodate the desired flow rate of each fuel. In other
embodiments, if the engine has sufficient space to mount two
separate fuel injection valves, the fuel injection assembly can
comprise two separate fuel injection valves, each housed in its own
body (as shown in FIG. 1). In yet another embodiment, the fuel
injection assembly can comprise at least one fuel injection valve
that injects one of the two fuels into a pre-chamber. Unlike in a
dual fuel engine where one of the fuels is injected into the intake
air and then enters the combustion chamber with the intake air
through the engine intake valve, with the subject fuel injection
assembly, after the engine intake valve is closed, both the pilot
fuel and the main fuel can be injected through the fuel injection
assembly into the combustion chamber either directly into the
combustion chamber or indirectly through a pre-chamber.
Injection of the two fuels through such a fuel injection assembly
requires the fuels to be raised to injection pressures sufficient
to overcome the late-cycle in-cylinder pressure, which is higher
than the air pressure in the intake air manifold and intake ports.
The advantages of such high-pressure direct-injection engine
systems include reduced tendency for engine knock, enabling higher
compression ratios, and no displacement of intake air by fuel.
Accordingly, high-pressure direct-injection is defined to refer to
systems that use a fuel injection assembly such as the embodiments
described herein.
While particular elements, embodiments and applications of the
present invention have been shown and described, it will be
understood, that the invention is not limited thereto since
modifications can be made by those skilled in the art without
departing from the scope of the present disclosure, particularly in
light of the foregoing teachings.
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